Forecasting Weather

Forecasting Weather Now that Meteorologists understand the factors that affect weather they must put all of this together to create weather maps and to determine weather patterns. Together weather maps and weather patterns are very helpful in forecasting the weather.

Weather Maps Graphically show temperature, barometric pressure, wind speed/direction, cloud cover and relative humidity. Also shows: Air masses Fronts hazardous conditions Created by putting together data from thousands of weather stations from all across the world.

Weather Map

Map Symbols Map symbols are used to help identify the conditions reported from each weather station.

Other Symbols

Weather Movement Weather moves from areas of high pressure to areas of low pressure within air masses. A huge body of air that has similar temperature, humidity and air pressure throughout it. Classified by two characteristics: Temperature humidity Warm or cold air masses depend on the temperature of the region over which the air mass forms.

Air Masses 4 general air masses Polar (P) Tropical (T) Continental (c) From the poles to 60° N or S latitude. Very cold air mass. Tropical (T) From the equator to 25° N or S latitude. Warm to hot air mass. Continental (c) Over any large land mass. Dry air mass. Marine (m) Over any large body of water. Wet air mass.

Combining Air Masses Maritime Tropical (mT) – warm, humid air masses that form over oceans near the tropics. Summer = hot and humid weather Winter = humid conditions that bring rain or snow. Maritime Polar (mP) – cool, humid air masses that form over the icy cold North Pacific and North Atlantic oceans. Affect the West Coast more than the East Coast Summer = cool, humid air brings fog, rain and cool temperatures to the West Coast.

Combining Air Masses 3. Continental Tropical (cT) – Hot, dry air masses that form only in the summer over dry areas of the southwest and northern Mexico. Cover the smallest area of all air masses! 4. Continental Polar (cP) – cool to cold and dry air masses that form over central and northern Canada and Alaska. Winter = clear, cold and dry air to much of North America. Arctic Air Masses (A) – bring bitterly cold weather with very low humidity. Polar Vortex

North American Air Masses

Fronts An area where two air masses meet and tend to not mix due to differences in temperature and density. Warm air masses = low densities and rise Cool air masses = higher densities and sink Colliding air masses often cause storms and changeable weather. 4 Types: Cold Front Warm Front Stationary Front Occluded Front

Front Symbols

Types of Fronts Cold Fronts – cold air masses meet and push under a warm air mass. Violent storms occur followed by fair, cool weather. Cumulonimbus Clouds

Types of Fronts 2. Warm Fronts – warm air masses overtake a cold air mass and moves over it. Rain is followed by hot, humid weather. Cirrus clouds followed by stratus clouds.

Types of Fronts 3. Stationary Fronts – warm air mass meets a cold air mass and no movement occurs Rain may fall for many days.

Types of Fronts 4. Occluded Front – A fast moving cold front overtakes a warm front, lifts it quickly causing large scale precipitation.

Understanding Weather Maps X cP

Understanding Weather Maps 78°F What is the temperature in Pittsburgh? What is the wind direction in NY City? What type of front is moving into X? What weather conditions should they be expecting? What is the wind speed at X? What type of air mass is moving into Pittsburgh? SE Warm Rain, hot & humid 20 cP – Continental Polar

Cyclones & Anticyclones Cyclones – areas of low pressure (L) that contain rising warm air. Greek for “wheel”. Cooler air will move in and take the place of the warm air causing air currents to spins counterclockwise causes rainy, stormy weather. Anticyclones – high pressure centers (H) of cold, dry air. Winds spiral clockwise causing clear, dry, fair weather.

Cyclones & Anticyclones

Hazardous Conditions Causes great human suffering and death. Responsible for sever damage to the environment, infrastructure of cities and town and private property. Types of Hazardous Conditions: Thunderstorms Hurricanes Tornadoes Winter Storms

Thunderstorms Thunderstorms form after severe heating of Earth’s surface. Form within large cumulonimbus clouds when warm air is forced upward at a cold front. Causes convection currents. Internal friction is created within these convection currents causing electric charges in the clouds. Lightning is the discharge of the electric charges. Thunder is the sound that rapidly heated air, from lightning, causes as it expands suddenly and explosively. Mechanical Energy

Tornadoes Develop in low, heavy cumulonimbus clouds during spring and early summer often in late afternoon. Rapidly whirling, funnel-shaped clouds that are short lived and develop over land from severe thunderstorms. Cyclone – counterclockwise rotation Over a lake or ocean = waterspout Occur ONLY in the United States The Great Plains has the greatest occurrence of tornadoes and is called “tornado alley”.

Hurricanes A tropical storm that has winds of 119 km/hr or higher and is about 600 km across. Develops over warm water as a low pressure area or tropical disturbance. Gets its energy from the warm, humid air at the ocean’s surface. Winds spiral inward, cyclone, toward the area of low pressure. Lowest air pressure in a hurricane is found in the center, the eye. Storm Surge – the dome of water that is pushed ashore where a hurricane lands. The cause of most damage and death!

Hurricane Categories

Winter Storms Snow falls when humid air cools below 0°C. Lake-Effect Snow is caused when land loses heat faster than water and a dry, cold air mass it picks up water vapor from the warmer bodies of water. Oswego, NY is one of the snowiest cities in the United States. Receives an average annual snowfall of over 200”.

Average Snowfall in New York